U.S. patent application number 14/776526 was filed with the patent office on 2016-02-11 for vehicle speed control system.
The applicant listed for this patent is JAGUAR LAND ROVER LIMITED. Invention is credited to Nick BROCKLEY, Andrew FAIRGRIEVE, James KELLY.
Application Number | 20160039415 14/776526 |
Document ID | / |
Family ID | 48226366 |
Filed Date | 2016-02-11 |
United States Patent
Application |
20160039415 |
Kind Code |
A1 |
BROCKLEY; Nick ; et
al. |
February 11, 2016 |
VEHICLE SPEED CONTROL SYSTEM
Abstract
A control system for a vehicle operable to implement a speed
control function, the control system being operable to: receive an
input of a target speed at which the vehicle is intended to travel;
determine an instantaneous value of a primary target speed torque
parameter corresponding to an amount of torque that should be
developed at a given position in a powertrain in order to control
the vehicle to travel at the target speed; and filter by means of
filter means a value of a torque parameter input thereto to
generate a filtered torque parameter value, the system being
operable to command the powertrain to develop at said position an
amount of torque corresponding to the filtered torque parameter
value, wherein the system is operable to input to the filter means
a secondary target speed torque parameter value determined in
dependence on the primary target speed torque parameter value and a
current value of filtered torque parameter generated by the filter
means.
Inventors: |
BROCKLEY; Nick; (Lichfield,
Staffordshire, GB) ; FAIRGRIEVE; Andrew; (Rugby,
Warwickshire, GB) ; KELLY; James; (Solihull, West
Midlands, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
JAGUAR LAND ROVER LIMITED |
Whitley, Coventry Warwickshire |
|
GB |
|
|
Family ID: |
48226366 |
Appl. No.: |
14/776526 |
Filed: |
March 7, 2014 |
PCT Filed: |
March 7, 2014 |
PCT NO: |
PCT/EP2014/054424 |
371 Date: |
September 14, 2015 |
Current U.S.
Class: |
701/94 |
Current CPC
Class: |
B60W 10/184 20130101;
B60W 2050/0027 20130101; B60W 50/06 20130101; B60W 2710/0666
20130101; B60W 10/06 20130101; B60W 2710/105 20130101; B60W 2540/10
20130101; B60W 2050/0008 20130101; B60W 10/18 20130101; B60W 30/143
20130101; B60W 2050/0052 20130101; B60W 2050/0056 20130101 |
International
Class: |
B60W 30/14 20060101
B60W030/14; B60W 10/18 20060101 B60W010/18; B60W 50/06 20060101
B60W050/06; B60W 10/06 20060101 B60W010/06 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 14, 2013 |
GB |
1304657.8 |
Claims
1. A control system for a vehicle operable to implement a speed
control function, the control system being operable to: receive an
input of a target speed at which the vehicle is intended to travel;
determine an instantaneous value of a primary target speed torque
parameter corresponding to an amount of torque that should be
developed at a given position in a powertrain in order to control
the vehicle to travel at the target speed; and filter by means of a
filter a value of a torque parameter input thereto to generate a
filtered torque parameter value, the system being operable to
command the powertrain to develop at said position an amount of
torque corresponding to the filtered torque parameter value,
wherein the system is operable to input to the filter a secondary
target speed torque parameter value determined in dependence on the
primary target speed torque parameter value and a current value of
filtered torque parameter generated by the filter.
2. A system according to claim 1 operable to determine the value of
the secondary target speed torque parameter in dependence on a
difference between the value of the primary target speed torque
parameter and the current value of the filtered torque
parameter.
3. A system according to claim 1 operable wherein if the value of
the primary target speed torque parameter is less than a current
value of the filtered torque parameter, the value of the secondary
target speed torque parameter is set to a value that is less than
the primary target speed torque parameter by an amount that is
determined in dependence on the primary target speed torque
parameter value and the current value of filtered torque
parameter.
4. A system according to claim 3 operable to input to the filter a
value of secondary target speed torque parameter that is less than
the primary target speed torque parameter by an amount
corresponding to the difference between the filtered torque
parameter value and the primary target speed torque parameter
value.
5. A system according to claim 3 operable to input to the filter a
value of secondary target speed torque parameter that is less than
the primary target speed torque parameter value by an amount
substantially equal to the difference between the filtered torque
parameter value and the primary target speed torque parameter
value, multiplied by a factor.
6. A system according to claim 1 operable such that if the value of
primary target speed torque parameter is greater than that of the
filtered torque parameter the value of secondary target speed
torque parameter input to the filter is increased to a value above
that of the primary target speed torque parameter value, the amount
of the increase being determined in dependence on the primary
target speed torque parameter value and the current value of
filtered torque parameter.
7. A system according to claim 6 operable to input to the filter a
value of secondary target speed torque parameter that is greater
than the primary target speed torque parameter value by an amount
substantially equal to the difference between the filtered torque
parameter value and the primary target speed torque parameter
value.
8. A system according to claim 6 operable to input to the filter a
value of secondary target speed torque parameter that is greater
than the primary target speed torque parameter value by an amount
substantially equal to the difference between the filtered torque
parameter value and the primary target speed torque parameter
value, multiplied by a factor.
9. A system according to claim 1 operable to limit an upper and
lower value of secondary target speed torque parameter input to the
filter to respective upper and lower saturation values.
10. A system according to claim 1 operable to input to the filter
the higher of the secondary target speed torque parameter value and
a value of a driver demanded torque parameter corresponding to a
setting of a user-operable accelerator control.
11. A system according to claim 1 wherein the filter is arranged to
subject the value of torque parameter input thereto to a low pass
filter.
12. A system according to claim 1 operable to receive a user input
of the target speed.
13. A vehicle comprising a control system according to claim 1.
14. A method of controlling a speed of a vehicle comprising:
receiving an input of a target speed at which the vehicle is
intended to travel; determining an instantaneous value of a primary
target speed torque parameter corresponding to an amount of torque
that should be developed at a given position in a powertrain in
order to control the vehicle to travel at the target speed;
filtering a value of a torque parameter input thereto to generate a
filtered torque parameter value; and commanding the powertrain to
develop at said position an amount of torque corresponding to the
filtered torque parameter value, wherein filtering the value of
torque parameter input thereto comprises filtering a secondary
target speed torque parameter value determined in dependence on the
primary target speed torque parameter value and a current value of
filtered torque parameter generated.
15. (canceled)
Description
FIELD OF THE INVENTION
[0001] The invention relates to a system for controlling the speed
of a vehicle. In particular, but not exclusively, the invention
relates to a system for controlling the speed of a land-based
vehicle which is capable of driving in a variety of different and
extreme terrains and conditions.
[0002] The content of co-pending UK patent application no
GB1214651.0 is hereby incorporated by reference.
BACKGROUND TO THE INVENTION
[0003] In known vehicle speed control systems, typically referred
to as cruise control systems, the vehicle speed is maintained
on-road once set by the user without further intervention by the
user so as to improve the driving experience for the user by
reducing workload.
[0004] The user selects a speed at which the vehicle is to be
maintained, and the vehicle is maintained at that speed for as long
as the user does not apply a brake or, in some systems, the clutch.
The cruise control system takes its speed signal from the
driveshaft or wheel speed sensors. When the brake or the clutch is
depressed, the cruise control system is disabled so that the user
can change the vehicle speed without resistance from the system. If
the user depresses the accelerator pedal the vehicle speed will
increase, but once the user removes his foot from the accelerator
pedal the vehicle reverts to the pre-set cruise speed.
[0005] More sophisticated cruise control systems are integrated
into the engine management system and may include an adaptive
functionality which takes into account the distance to the vehicle
in front using a radar-based system. For example, the vehicle may
be provided with a forward-looking radar detection system so that
the speed and distance of the vehicle in front is detected and a
safe following speed and distance is maintained automatically
without the need for user input. If the lead vehicle slows down, or
another object is detected by the radar detection system, the
system sends a signal to the engine or the braking system to slow
the vehicle down accordingly.
[0006] Such systems are usually operable only above a certain
speed, typically around 15-20 mph, and are ideal in circumstances
in which the vehicle is travelling in steady traffic conditions,
and particularly on highways or motorways. In congested traffic
conditions, however, where vehicle speed tends to vary widely,
cruise control systems are ineffective, and especially where the
systems are inoperable because of a minimum speed requirement. A
minimum speed requirement is often imposed on cruise control
systems so as to reduce the likelihood of low speed collision, for
example when parking. Such systems are therefore ineffective in
certain driving conditions (e.g. low speed) and are set to be
automatically disabled in circumstances in which a user may not
consider it to be desirable to do so.
[0007] Known cruise control systems also cancel in the event that a
wheel slip event is detected requiring intervention by a traction
control system (TCS) or stability control system (SCS).
Accordingly, they are not well suited to maintaining vehicle
progress when driving in off road conditions where such events may
be relatively common.
[0008] It is also known to provide a control system for a motor
vehicle for controlling one or more vehicle subsystems. U.S. Pat.
No. 7,349,776, the content of which is hereby incorporated by
reference, discloses a vehicle control system comprising a
plurality of subsystem controllers including an engine management
system, a transmission controller, a steering controller, a brakes
controller and a suspension controller. The subsystem controllers
are each operable in a plurality of subsystem function modes. The
subsystem controllers are connected to a vehicle mode controller
which controls the subsystem controllers to assume a required
function mode so as to provide a number of driving modes for the
vehicle. Each of the driving modes corresponds to a particular
driving condition or set of driving conditions, and in each mode
each of the sub-systems is set to the function mode most
appropriate to those conditions. Such conditions are linked to
types of terrain over which the vehicle may be driven such as
grass/gravel/snow, mud and ruts, rock crawl, sand and a highway
mode known as `special programs off` (SPO). The vehicle mode
controller may be referred to as a Terrain Response (TR) (.RTM.)
System or controller.
[0009] It is desirable to provide a speed control system capable of
controlling vehicle speed at relatively low speeds and whilst
driving in off road conditions.
STATEMENTS OF INVENTION
[0010] Embodiments of the invention may be understood with
reference to the appended claims.
[0011] Aspects of the present invention provide a system, a vehicle
and a method.
[0012] In one aspect of the invention for which protection is
sought there is provided a control system for a vehicle operable to
implement a speed control function, the control system being
operable to: [0013] receive an input of a target speed at which the
vehicle is intended to travel; [0014] determine an instantaneous
value of a primary target speed torque parameter corresponding to
an amount of torque that should be developed at a given position in
a powertrain in order to control the vehicle to travel at the
target speed; and [0015] filter by means of filter means a value of
a torque parameter input thereto to generate a filtered torque
parameter value, [0016] the system being operable to command the
powertrain to develop at said position an amount of torque
corresponding to the filtered torque parameter value, [0017]
wherein the system is operable to input to the filter means a
secondary target speed torque parameter value determined in
dependence on the primary target speed torque parameter value and a
current value of filtered torque parameter generated by the filter
means.
[0018] The primary target speed torque parameter may have a value
substantially equal to the amount of torque required to control the
vehicle to travel at the target speed. Alternatively the primary
target speed torque parameter may have a value indicative of the
amount of torque required.
[0019] By given position of the powertrain is meant any suitable
position of the powertrain, such as an engine output shaft for a
vehicle having an engine, a gearbox or transmission input shaft,
output shaft, drive shaft, one or more road wheels or any other
suitable location of the powertrain.
[0020] The present inventors have recognised that in vehicles not
according to an embodiment of the present invention, a substantial
difference may be observed in respect of the responsiveness of a
vehicle to changes in speed depending on whether speed control is
active. This can result in a reduction of driver confidence in the
speed control system.
[0021] Embodiments of the present invention have the advantage that
a difference in a response of a vehicle to changes in powertrain
torque demand in dependence on whether or not the control system is
implementing the speed control function may be reduced. This
feature has the advantage that driver confidence in the speed
control function may be enhanced.
[0022] Embodiments of the invention may have at least two
advantages. The first is that, when speed control is performed by
the control system, a responsiveness of the powertrain to changes
in torque demanded by the speed control function may be enhanced,
since any phase lag between the filtered torque parameter value and
target speed torque parameter value may be reduced.
[0023] The second is that, if a driver over-rides speed control by
demanding more torque than that corresponding to the target speed
torque parameter value, for example by depressing an accelerator
pedal or the like by a sufficient amount, when the driver
subsequently stops over-riding speed control the filtered torque
parameter value falls to the primary target speed torque parameter
value much more quickly.
[0024] For example, if a driver is travelling without speed control
active at 10 kph and wishes to reduce vehicle speed to 5 kph, the
driver might temporarily release an accelerator control such as an
accelerator pedal and allow vehicle speed to fall to a value close
to the target speed. The driver might then actuate the accelerator
pedal to maintain the target speed. Engine braking might therefore
be provided by the powertrain to slow the vehicle during the period
in which the accelerator pedal is in a released condition. In other
words, negative torque may be developed by the powertrain to slow
the vehicle, resulting in a more rapid decrease in vehicle
speed.
[0025] In contrast, it speed control by the control system is
active and the driver over-rides the speed control function by
demanding more powertrain torque than that requested by the speed
control function, for example in order to move more quickly past a
particular location, and then releases the accelerator pedal and
allows the control system to resume vehicle control, the amount of
torque demanded of the powertrain whilst the vehicle decelerates
may not fall towards a value corresponding to a released
accelerator pedal position as quickly as in the case where speed
control is not active. Accordingly the driver may perceive the
vehicle speed to be `floating`, i.e. falling too slowly, and the
vehicle relatively unresponsive to the release of the accelerator
pedal by the driver.
[0026] Embodiments of the present invention overcome this problem
by modifying the value of a torque parameter input to the filter
means according to the difference between the primary target speed
torque parameter and the filtered torque parameter value. This has
the effect that the filtered torque value tends towards the primary
target speed torque value more quickly.
[0027] Advantageously the system may be operable to determine the
value of the secondary target speed torque parameter in dependence
on a difference between the value of the primary target speed
torque parameter and the current value of the filtered torque
parameter.
[0028] The system may be operable wherein if the value of the
primary target speed torque parameter is less than a current value
of the filtered torque parameter, the value of the secondary target
speed torque parameter is set to a value that is less than the
primary target speed torque parameter by an amount that is
determined in dependence on the primary target speed torque
parameter value and the current value of filtered torque
parameter.
[0029] This feature has the advantage that a rate at which the
amount of torque developed by the powertrain decreases to the
primary target speed torque may be made to correspond more closely
to that which would be experienced in the event a driver were to
slow the vehicle to the target speed without using the control
system speed control functionality.
[0030] The amount by which the value of torque parameter applied to
the filter means is less than the target speed torque parameter may
be an amount substantially equal to the difference between the
value of target speed torque parameter and the current value of
filtered torque parameter. Alternatively the amount may be a
multiple of the difference. The multiple may be less than 1 or
greater than one, such as 0.5, 1.5, 2, 3, 4, 5 or any other
suitable value. Thus the amount may be non-integer. Other
arrangements are also useful.
[0031] The system may be operable to input to the filter means a
value of secondary target speed torque parameter that is less than
the primary target speed torque parameter by an amount
corresponding to the difference between the filtered torque
parameter value and the primary target speed torque parameter
value.
[0032] The system may be operable to input to the filter means a
value of secondary target speed torque parameter that is less than
the primary target speed torque parameter value by an amount
substantially equal to the difference between the filtered torque
parameter value and the primary target speed torque parameter
value, multiplied by a factor.
[0033] The factor may be less than or greater than 1.
[0034] The system may be operable such that if the value of primary
target speed torque parameter is greater than that of the filtered
torque parameter the value of secondary target speed torque
parameter input to the filter means is increased to a value above
that of the primary target speed torque parameter value, the amount
of the increase being determined in dependence on the primary
target speed torque parameter value and the current value of
filtered torque parameter.
[0035] The system may be operable to input to the filter means a
value of secondary target speed torque parameter that is greater
than the primary target speed torque parameter value by an amount
substantially equal to the difference between the filtered torque
parameter value and the primary target speed torque parameter
value.
[0036] The system may be operable to input to the filter means a
value of secondary target speed torque parameter that is greater
than the primary target speed torque parameter value by an amount
substantially equal to the difference between the filtered torque
parameter value and the primary target speed torque parameter
value, multiplied by a factor.
[0037] The system may be operable to limit an upper and lower value
of secondary target speed torque parameter input to the filter
means to respective upper and lower saturation values.
[0038] This feature has the advantage that extreme excursions in
the value of powertrain torque parameter when under speed control
may be prevented. Thus, whilst it has been stated above that the
modifier means is arranged such that if the value of target speed
torque parameter is less than a current value of filtered torque
parameter, the modifier means reduces the value of torque parameter
output thereby to the filter means, the modifier means will not
reduce the value of torque parameter output thereby to the filter
means below a prescribed value. Similarly, the modifier means will
not increase the value of torque parameter output thereby to a
value that is above the upper saturation value.
[0039] The system may be operable to input to the filter means the
higher of the secondary target speed torque parameter value and a
value of a driver demanded torque parameter corresponding to a
setting of a user-operable accelerator control.
[0040] Thus, the same filter may be used to filter torque values
demanded by the control system and by a driver.
[0041] This feature eliminates the requirement to provide a control
system that takes into account functions associated with the filter
means of the particular vehicle in which the control system is
installed. Thus the same control system may be installed in a range
of different vehicles each having tilter means with different
respective characteristics.
[0042] It is to be understood that the filter means is typically
employed in vehicles regardless of whether a speed control function
is provided and is arranged to mitigate the effects of driveline or
powertrain shunt when a user varies powertrain torque demand (e.g.
by varying accelerator pedal position). By employing the filter
means when speed control is in progress, a workload on the designer
of the speed control function is reduced since the factors taken
into account by the filter means do not need to be taken into
account by the speed control function to the same extent, if at
all. Thus, issues such as mitigation of powertrain shunt may be
taken into account by the filter means allowing similar or
substantially identical speed control functions to be employed in a
range of different vehicles having powertrains with different
characteristics such as stiffness and resonant frequencies.
[0043] The filter means may be arranged to subject the value of
torque parameter input thereto to a low pass filter.
[0044] The system may be operable to receive a user input of the
target speed.
[0045] In a further aspect of the invention for which protection is
sought there is provided a vehicle comprising a control system
according to a preceding aspect.
[0046] Embodiments of the present invention are useful in a range
of different types of vehicles including vehicles having a single
engine such as a single internal combustion engine as the source of
propulsion, in hybrid electric vehicles and in electric
vehicles.
[0047] In one aspect of the invention for which protection is
sought there is provided a method of controlling a speed of a
vehicle comprising: [0048] receiving an input of a target speed at
which the vehicle is intended to travel; determining an
instantaneous value of a primary target speed torque parameter
corresponding to an amount of torque that should be developed at a
given position in a powertrain in order to control the vehicle to
travel at the target speed; filtering by filter means a value of a
torque parameter input thereto to generate a filtered torque
parameter value; and commanding the powertrain to develop at said
position an amount of torque corresponding to the filtered torque
parameter value, wherein filtering by the filter means the value of
torque parameter input thereto comprises filtering a secondary
target speed torque parameter value determined in dependence on the
primary target speed torque parameter value and a current value of
filtered torque parameter generated by the filter means.
[0049] In one aspect of the invention for which protection is
sought there is provided a control system for a vehicle operable to
implement a speed control function, the control system comprising:
[0050] means for receiving a user input of a target speed at which
the vehicle is intended to travel; [0051] target speed torque
determining means for determining an instantaneous value of torque,
target speed torque, that should be applied to one or more wheels
of the vehicle by a powertrain in order to control the vehicle to
travel at the target speed; and [0052] filter means operable to
filter a value of torque input thereto to generate a filtered
torque value, [0053] the system being operable to command the
powertrain to apply to the one or more wheels an amount of torque
corresponding to the filtered torque value, [0054] wherein the
system further comprises modifier means operable to receive the
instantaneous value of target speed torque generated by the target
speed torque determining means and to input to the filter means a
value of torque determined in dependence on a difference between
the target speed torque value and a current value of filtered
torque.
[0055] In one aspect of the invention for which protection is
sought there is provided a control system for a vehicle operable to
implement a speed control function, the control system comprising:
[0056] means for receiving a user input of a target speed at which
the vehicle is intended to travel; [0057] target speed torque
parameter determining means for determining an instantaneous value
of a target speed torque parameter corresponding to an amount of
torque that should be developed at a given position in a powertrain
in order to control the vehicle to travel at the target speed; and
[0058] filter means operable to filter a value of a torque
parameter input thereto to generate a filtered torque parameter
value, [0059] the system being operable to command the powertrain
to develop at said position an amount of torque corresponding to
the filtered torque parameter value, [0060] wherein the system
further comprises modifier means operable to receive the
instantaneous value of target speed torque parameter generated by
the target speed torque parameter determining means and to input to
the filter means a value determined in dependence on the target
speed torque parameter value and a current value of filtered torque
parameter generated by the filter means.
[0061] Advantageously the modifier means is operable to input to
the filter means a value of torque parameter determined in
dependence on a difference between the target speed torque
parameter value and the current value of filtered torque
parameter.
[0062] The modifier means may be arranged such that if the value of
the target speed torque parameter is less than a current value of
the filtered torque parameter, the modifier means reduces the value
of torque parameter output thereby to the filter means to a value
below that of the target speed torque parameter, the amount of the
reduction being determined in dependence on the target speed torque
parameter value and the current value of filtered torque
parameter.
[0063] The system may be operable to apply to the filter means a
value of torque parameter that is less than the target speed torque
parameter value by an amount substantially equal to the difference
between the substantially instant filtered torque parameter value
and the substantially instant target speed torque parameter
value.
[0064] Advantageously the modifier means may be arranged such that
if the value of target speed torque parameter is greater than that
of the filtered torque parameter the modifier means increases the
value of torque parameter output thereby to the filter means to a
value above that of the target speed torque parameter value, the
amount of the increase being determined in dependence on the target
speed torque parameter value and the current value of filtered
torque parameter.
[0065] The system may be operable to apply to the filter means a
value of powertrain torque parameter that is greater than the
target speed torque parameter value by an amount substantially
equal to the difference between the substantially instant filtered
torque parameter value and the substantially instant target speed
torque parameter value.
[0066] The modifier means may be operable to limit an upper and
lower value of torque parameter output thereby to respective upper
and lower saturation values.
[0067] Advantageously the system may comprise means for generating
a value of driver demanded torque parameter in dependence on a
position of a user operable accelerator control, the system being
operable to apply to the filter means the higher of driver demanded
torque parameter value and the value of torque parameter output by
the modifier means.
[0068] The filter means may be arranged to subject the value of
torque parameter input thereto to a low pass filter.
[0069] In a further aspect of the invention for which protection is
sought there is provided a vehicle comprising a control system
according to a preceding aspect.
[0070] In another aspect of the invention for which protection is
sought there is provided a method of controlling a speed of a
vehicle comprising: [0071] receiving a user input of a target speed
at which the vehicle is intended to travel; [0072] determining an
instantaneous value of a target speed torque parameter
corresponding to an amount of torque that should be developed at a
given position in a powertrain in order to control the vehicle to
travel at the target speed; [0073] filtering by filter means a
value of a torque parameter input thereto to generate a filtered
torque parameter value; and [0074] commanding the powertrain to
develop at said position an amount of torque corresponding to the
filtered torque parameter value, [0075] wherein filtering by the
filter means the value of torque parameter input thereto comprises
filtering a torque parameter value determined in dependence on the
target speed torque parameter value and a current value of filtered
torque parameter generated by the filter means.
[0076] It is to be understood that the target speed may also be
referred to as a `set-speed` and the terms `target speed` and
`set-speed` are used interchangeably herein.
[0077] In one aspect of the invention there is provided a speed
control system modifier operable to receive from a speed control
system a speed control signal corresponding to a required amount of
torque and a signal from a torque filter corresponding to a
filtered torque value, the modifier being operable to output to the
torque filter a torque signal that is determined in dependence on
the value of speed control signal and filtered torque value. The
signal may be determined by subtracting from the speed control
signal a value corresponding to the difference between the speed
control signal and the filtered torque value. The signal may be
substantially equal to this difference multiplied by a factor.
[0078] It will be appreciated that preferred and/or optional
features of any one aspect of the invention may be incorporated
alone or in appropriate combination within the any other aspect of
the invention also.
BRIEF DESCRIPTION OF THE DRAWINGS
[0079] The invention will now be described by way of example only
with reference to the following figures in which:
[0080] FIG. 1 is a schematic illustration of a vehicle according to
an embodiment of the invention in plan view;
[0081] FIG. 2 shows the vehicle of FIG. 1 in side view;
[0082] FIG. 3 is a high level schematic diagram of an embodiment of
the vehicle speed control system of the present invention,
including a cruise control system and a low-speed progress control
system;
[0083] FIG. 4 is a flow diagram to illustrate the interaction
between the cruise control system and the low-speed progress
control system in FIG. 3;
[0084] FIG. 5 is a schematic diagram of further features of the
vehicle speed control system in FIG. 3;
[0085] FIG. 6 illustrates a steering wheel and brake and
accelerator pedals of a vehicle according to an embodiment of the
present invention;
[0086] FIG. 7 shows a portion of a vehicle speed control system
according to an embodiment of the present invention;
[0087] FIG. 8 shows (a) a portion of a vehicle speed control system
not being a system according to an embodiment of the present
invention and (b) a plot of filtered powertrain torque as a
function of time following driver intervention; and
[0088] FIG. 9 shows a portion of a vehicle speed control system
according to an embodiment of the present invention in more
detail.
DETAILED DESCRIPTION
[0089] References herein to a block such as a function block are to
be understood to include reference to software code for performing
the function or action specified in which an output is provided
responsive to one or more inputs. The code may be in the form of a
software routine or function called by a main computer program, or
may be code forming part of a flow of code not being a separate
routine or function. Reference to function block is made for ease
of explanation of the manner of operation of the controller.
[0090] FIG. 1 shows a vehicle 100 according to an embodiment of the
invention having a powertrain 129. The powertrain 129 includes an
engine 121 that is connected to a driveline 130 having an automatic
transmission 124. Embodiments of the present invention are suitable
for use in vehicles with manual transmissions, continuously
variable transmissions or any other suitable transmission.
[0091] The driveline 130 is arranged to drive a pair of front
vehicle wheels 111,112 by means of a front differential 137 and a
pair of front drive shafts 118. The driveline 130 also comprises an
auxiliary driveline portion 131 arranged to drive a pair of rear
wheels 114, 115 by means of an auxiliary driveshaft or prop-shaft
132, a rear differential 135 and a pair of rear driveshafts 139.
Embodiments of the invention are suitable for use with vehicles in
which the transmission is arranged to drive only a pair of front
wheels or only a pair of rear wheels (i.e. front wheel drive
vehicles or rear wheel drive vehicles) or selectable two wheel
drive/four wheel drive vehicles. In the embodiment of FIG. 1 the
transmission 124 is releasably connectable to the auxiliary
driveline portion 131 by means of a power transfer unit (PTU) 131P,
allowing selectable two wheel drive or four wheel drive operation.
It is to be understood that embodiments of the invention may be
suitable for vehicles having more than four wheels or where only
two wheels are driven, for example two wheels of a three wheeled
vehicle or four wheeled vehicle or a vehicle with more than four
wheels.
[0092] A control system for the vehicle engine 121 includes a
central controller, referred to as a vehicle control unit (VCU) 10,
a powertrain controller 11, a brake controller 13 and a steering
controller 170C. The brake controller 13 forms part of a braking
system 22 (FIG. 3). The VCU 10 receives and outputs a plurality of
signals to and from various sensors and subsystems (not shown)
provided on the vehicle. The VCU 10 includes a low-speed progress
(LSP) control system 12 shown in FIG. 3 and a stability control
system (SCS) 14, the latter being a known component of existing
vehicle control systems. The SCS 14 improves the safety of the
vehicle 100 by detecting and managing loss of traction. When a
reduction in traction or steering control is detected, the SCS 14
is operable automatically to command a brake controller 13 to apply
one or more brakes of the vehicle to help to steer the vehicle 100
in the direction the user wishes to travel. In the embodiment shown
the SCS 14 is implemented by the VCU 10. In some alternative
embodiments the SCS 14 may be implemented by the brake controller
13. Further alternatively, the SCS 14 may be implemented by a
separate controller.
[0093] Although not shown in detail in FIG. 3, the VCU 10 further
includes a Dynamic Stability Control (DSC) function block, a
Traction Control (TC) function block, an Anti-Lock Braking System
(ABS) function block and a Hill Descent Control (HDC) function
block. These function blocks are implemented in software code run
by a computing device of the VCU 10 and provide outputs indicative
of, for example, DSC activity, TC activity, ABS activity, brake
interventions on individual wheels and engine torque requests from
the VCU 10 to the engine 121 in the event a wheel slip event
occurs. Each of the aforementioned events indicate that a wheel
slip event has occurred. Other vehicle sub-systems such as a roll
stability control system or the like may also be useful.
[0094] The vehicle 100 also includes a cruise control system 16
which is operable to automatically maintain vehicle speed at a
selected speed when the vehicle is travelling at speeds in excess
of 30 kph. The cruise control system 16 is provided with a cruise
control HMI (human machine interface) 18 by which means the user
can input a target vehicle speed to the cruise control system 16 in
a known manner. In one embodiment of the invention, cruise control
system input controls are mounted to a steering wheel 171 (FIG. 6).
Depression of a `set-speed` control 173 sets the set-speed to the
current vehicle speed. Depression of a `+` button 174 allows the
set-speed to be increased whilst depression of a `-` button 175
allows the set-speed to be decreased. In some embodiments, if the
cruise control system 16 is not active when the `+` button 174 is
depressed, the cruise control system 16 is activated.
[0095] The cruise control system 16 monitors vehicle speed and any
deviation from the target vehicle speed is adjusted automatically
so that the vehicle speed is maintained at a substantially constant
value, typically in excess of 30 kph. In other words, the cruise
control system is ineffective at speeds lower than 30 kph. The
cruise control HMI 18 may also be configured to provide an alert to
the user about the status of the cruise control system 16 via a
visual display of the HMI 18.
[0096] The LSP control system 12 provides a speed-based control
system for the user which enables the user to select a very low
target speed at which the vehicle can progress without any pedal
inputs being required by the user. This low-speed progress control
function is not provided by the on-highway cruise control system 16
which operates only at speeds above 30 kph. Furthermore, known
on-highway cruise control systems including the present system 16
are configured so that, in the event that the user depresses the
brake or the clutch, the cruise control function is cancelled and
the vehicle 100 reverts to a manual mode of operation which
requires user pedal input to maintain vehicle speed. In addition,
detection of a wheel slip event, as may be initiated by a loss of
traction, also has the effect of cancelling the cruise control
function.
[0097] The LSP control system 12 is operable to apply selective
powertrain, traction control and braking actions to the wheels of
the vehicle, collectively or individually, to maintain the vehicle
100 at the desired speed. It is to be understood that if the
vehicle 100 is operating in a two wheel drive mode in which only
front wheels 111, 112 are driven, the control system 12 may be
prevented from applying drive torque to rear wheels 113, 114 of the
vehicle 100.
[0098] The user inputs the desired target speed to the LSP control
system 12 via a low-speed progress control HMI (LSP HMI) 20 (FIG.
1, FIG. 3). The LSP control system 12 operates at vehicle speeds
typically below about 50 kph but does not activate until vehicle
speed drops to below 30 kph when the cruise control system of the
vehicle becomes ineffective. The LSP control system 12 is
configured to operate independently of a traction event, i.e. the
system 12 does not cancel speed control upon detection of wheel
slip. Rather, the LSP control system 12 actively manages vehicle
behaviour and in this way, at least, differs from the functionality
of the cruise control system 16, as will be described in further
detail below.
[0099] The LSP control HMI 20 is provided in the vehicle cabin so
as to be readily accessible to the user. The user of the vehicle is
able to input to the LSP control system 12, via the LSP HMI 20, an
indication of the speed at which the user desires the vehicle to
travel (referred to as "the target speed"). The LSP HMI 20 also
includes a visual display upon which information and guidance can
be provided to the user about the status of the LSP control system
12.
[0100] The LSP control system 12 receives an input from the braking
system 22 of the vehicle indicative of the extent to which the user
has applied braking by means of a brake pedal 163. The LSP control
system 12 also receives an input from an accelerator pedal 161
indicative of the extent to which the user has depressed the
accelerator pedal 161. An input is also provided to the LSP control
system 12 from the transmission or gearbox 124. This input may
include signals representative of, for example, the speed of an
output shaft of the gearbox 124, torque converter slip and a gear
ratio request. Other inputs to the LSP control system 12 include an
input from the cruise control HMI 18 which is representative of the
status (ON/OFF) of the cruise control system 16, and an input from
the LSP control HMI 20 which is representative of the status of the
LSP control function.
[0101] The cruise control HMI 18 and the LSP HMI 20 have input
controls provided on a steering wheel of the vehicle for
convenience of operation by the user.
[0102] FIG. 6 shows the steering wheel 171 of the vehicle 100 of
FIG. 1 in more detail, together with the accelerator and brake
pedals 161, 163. As noted above, the steering wheel 171 bears user
operable input controls of the cruise control HMI 18 and LSP
control HMI 20. As in the case of a conventional vehicle, the
steering wheel 171 has a `set-speed` control 173, actuation of
which enables a user to activate the cruise control system 16 to
maintain the current vehicle speed. The wheel 171 also has a `LSP`
control activation button 172 for activating the LSP control system
12 and a resume button 173R. The resume button 173R may be used to
control both the `on-highway` cruise control system 16 when driving
on road, and the LSP control system 12 when driving off-road, to
resume a previously set (user defined) set-speed.
[0103] If the vehicle is operating on-highway, depression of
set-speed control 173 causes the cruise control system 16 to
activate provided the current vehicle speed is within the operating
range of the cruise control system 16. Depression of the `+`
control 174 causes the cruise control system 16 to increase the
set-speed whilst depression of the `-` control 175 causes the
cruise control system 16 to decrease the set-speed. It will be
appreciated that "+" and `-` controls may be on a single button in
some arrangements, such as a rocker-type button. In some
embodiments, the `+` control 174 may function as a `set-speed`
control, in which case set-speed control 173 may be eliminated.
[0104] If the vehicle is operating off-highway, depression of
set-speed control 173 causes the LSP control system 12 to activate
and operate as described above, provided vehicle speed is within
the operating range of the LSP control system 12.
[0105] In some embodiments, the system may further comprise a
`cancel` button operable to cancel speed control by the LSP control
system 12. In some embodiments, the LSP system may be in either one
of an active condition or a standby condition. In the present
embodiment the LSP control system 12 is also operable to assume an
intermediate condition in which vehicle speed control by the LSP
control system 12 is suspended but a hill descent control (HDC)
system or the like may remain active if already active. Other
arrangements are also useful.
[0106] With the LSP control system 12 active, the user may increase
or decrease the vehicle set-speed by means of the `+` and `-`
buttons 174, 175. In addition, the user may also increase or
decrease the vehicle set-speed by lightly pressing the accelerator
or brake pedals 161, 163 respectively. In some embodiments, with
the LSP control system 12 active the `+` and `-` buttons 174, 175
are disabled. This latter feature may prevent changes in set-speed
by accidental pressing of one of these buttons, for example when
negotiating difficult terrain where relatively large and frequent
changes in steering angle may be required. Other arrangements are
also useful.
[0107] FIG. 4 shows a flow process to illustrate the interaction
between the cruise control system 18 and the LSP control system 12.
If cruise control is active when the user tries to activate the LSP
control system 12 via the LSP control HMI 20, a signal is sent to
the cruise control system 16 to cancel the speed control routine.
The LSP control system 12 is then initiated and the vehicle speed
is maintained at the target speed selected by the user via the LSP
HMI 20. It is also the case that if the LSP control system 12 is
active, operation of the cruise control system 16 is inhibited. The
two systems 12, 16 therefore operate independently of one another,
so that only one can be operable at any one time, depending on the
speed at which the vehicle is travelling.
[0108] In some embodiments, the cruise control system 16 may hand
over vehicle speed control to the LSP control system 12 if a user
reduces set-speed of the vehicle 100 to a value within the
operating speed range of the LSP control system 12. Similarly, in
some embodiments the LSP control system 16 may hand over vehicle
speed control to the cruise control system 16 if a user raises
vehicle set-speed to a value that is within the operating range of
the cruise control system 16. Other arrangements are also
useful.
[0109] In some embodiments, the cruise control HMI 18 and the LSP
control HMI 20 may be configured within the same hardware so that,
for example, the speed selection is input via the same hardware,
with one or more separate switches being provided to switch between
the LSP input and the cruise control input.
[0110] FIG. 5 illustrates the means by which vehicle speed is
controlled in the LSP control system 12. As described above, a
speed selected by a user (set-speed) is input to the LSP control
system 12 via the LSP control HMI 20. A vehicle speed sensor 34
associated with the powertrain 129 (shown in FIG. 1) provides a
signal 36 indicative of vehicle speed to the LSP control system 12.
The LSP control system 12 includes a comparator 28 which compares
the set-speed (also referred to as a `target speed` 38) selected by
the user with the measured speed 36 and provides an output signal
30 indicative of the comparison. The output signal 30 is provided
to an evaluator unit 40 of the VCU 10 which interprets the output
signal 30 as either a demand for additional torque to be applied to
the vehicle wheels 111-115, or for a reduction in torque applied to
the vehicle wheels 111-115, depending on whether the vehicle speed
needs to be increased or decreased to maintain the speed that has
been selected by the user. An increase in torque is generally
accomplished by increasing the amount of powertrain torque
delivered to a given position of the powertrain, for example an
engine output shaft, a wheel or any other suitable location. A
decrease in torque to a value that is less positive or more
negative may be accomplished by decreasing powertrain torque
delivered to a wheel and/or by increasing a braking force on a
wheel. It is to be understood that in some embodiments in which a
powertrain 129 has an electric machine operable as a generator,
negative torque may be applied by the powertrain 129 to one or more
wheels. It is to be understood that a brake controller 13 may
nevertheless be involved in determining whether brake torque is
required to be provided by an electric machine of a powertrain 129,
and whether brake torque should be provided by an electric machine
or a friction-based foundation braking system 22.
[0111] An output 42 from the evaluator unit 40 is provided to the
powertrain controller 11 and brake controller 13 which in turn
control a net torque applied to the vehicle wheels 111-115. The net
torque may be increased or decreased depending on whether there is
a positive or negative demand for torque from the evaluator unit
40. Thus, in order to initiate application of the necessary
positive or negative torque to the wheels, the evaluator unit 40
may command that additional power is applied to the vehicle wheels
and/or that a braking force is applied to the vehicle wheels,
either or both of which may be used to implement the change in
torque that is necessary to maintain the target vehicle speed. In
the illustrated embodiment the torque is applied to the vehicle
wheels individually so as to maintain the target vehicle speed, but
in another embodiment torque may be applied to the wheels
collectively to maintain the target speed. In some embodiments, the
powertrain controller 11 may be operable to control an amount of
torque applied to one or more wheels by controlling a driveline
component such as a rear drive unit, front drive unit, differential
or any other suitable component. For example, one or more
components of the driveline 130 may include one or more clutches
operable to allow an amount of torque applied to one or more wheels
to be varied. Other arrangements are also useful.
[0112] Where a powertrain 129 includes one or more electric
machines, for example one or more propulsion motors and/or
generators, the powertrain controller 11 may be operable to
modulate torque applied to one or more wheels by means of one or
more electric machines. In some embodiments, the one or more
electric machines may be operable as either a propulsion motor or a
generator under the control of the powertrain controller 11. Thus
the powertrain controller 11 may in some embodiments be controlled
to apply more positive or more negative torque to one or more
wheels by means of an electric machine.
[0113] The LSP control system 12 also receives a signal 48
indicative of a wheel slip event having occurred. This may be the
same signal 48 that is supplied to the on-highway cruise control
system 16 of the vehicle, and which in the case of the latter
triggers an override or inhibit mode of operation in the on-highway
cruise control system 16 so that automatic control of the vehicle
speed by the on-highway cruise control system 16 is suspended or
cancelled. However, the LSP control system 12 is not arranged to
cancel or suspend operation in dependence on receipt of a wheel
slip signal 48 indicative of wheel slip. Rather, the system 12 is
arranged to monitor and subsequently manage wheel slip so as to
reduce driver workload. During a slip event, the LSP control system
12 continues to compare the measured vehicle speed with the desired
vehicle speed as input by the user, and continues to control
automatically the torque applied across the vehicle wheels so as to
maintain vehicle speed at the selected value. It is to be
understood therefore that the LSP control system 12 is configured
differently to the cruise control system 16, for which a wheel slip
event has the effect of overriding the cruise control function so
that manual operation of the vehicle must be resumed, or the cruise
control function reset.
[0114] A further embodiment of the invention (not shown) is one in
which the vehicle is provided with a wheel slip signal 48 derived
not just from a comparison of wheel speeds, but further refined
using sensor data indicative of the vehicle's speed over ground.
Such speed over ground determination may be made via global
positioning (GPS) data, or via a vehicle mounted radar or laser
based system arranged to determine the relative movement of the
vehicle and the ground over which it is travelling. A camera system
may be employed for determining speed over ground in some
embodiments.
[0115] At any stage of the LSP control process the user can
override the function by depressing the accelerator pedal 161
and/or brake pedal 163 to adjust the vehicle speed in a positive or
negative sense. However, in the event that a wheel slip event is
detected via signal 48, the LSP control system 12 remains active
and control of vehicle speed by the LSP control system 12 is not
suspended. As shown in FIG. 5, this may be implemented by providing
a wheel slip event signal 48 to the LSP control system 12 which is
then managed by the LSP control system 12. In the embodiment shown
in FIG. 1 the SCS 14 generates the wheel slip event signal 48 and
provides it to the LSP control system 12 and cruise control system
16.
[0116] A wheel slip event is triggered when a loss of traction
occurs at any one of the vehicle wheels. Wheels and tyres may be
more prone to losing traction when travelling on snow, ice or sand
and/or on steep gradients or cross-slopes, for example, or in
environments where the terrain is more uneven or slippery compared
with driving on a highway in normal on-road conditions. Embodiments
of the present invention therefore find particular benefit when the
vehicle is being driven in an off-road environment, or in
conditions in which wheel slip may commonly occur. Manual operation
by the user in such conditions can be a difficult and often
stressful experience and may result in an uncomfortable ride.
Embodiments of the present invention enable continued progress to
be made at a relatively low target speed without the need for user
intervention.
[0117] The vehicle 100 is also provided with additional sensors
(not shown) which are representative of a variety of different
parameters associated with vehicle motion and status. These may be
inertial systems unique to the speed control system or part of an
occupant restraint system or any other sub-system which may provide
data from sensors such as gyros and/or accelerometers that may be
indicative of vehicle body movement and may provide a useful input
to the LSP control system 12. The signals from the sensors provide,
or are used to calculate, a plurality of driving condition
indicators (also referred to as terrain indicators) which are
indicative of the nature of the terrain conditions over which the
vehicle is travelling. The signals are provided to the VCU 10 which
determines the most appropriate control mode for the various
subsystems on the basis of the terrain indicators, and
automatically controls the subsystems accordingly. This aspect of
the invention is described in further detail in our co-pending
patent application nos. GB1111288.5, GB1211910.3 and GB1202427.9,
the contents of each of which is incorporated herein by
reference.
[0118] The sensors (not shown) on the vehicle include, but are not
limited to, sensors which provide continuous sensor outputs to the
VCU 10, including wheel speed sensors, as mentioned previously and
as shown in FIG. 5, an ambient temperature sensor, an atmospheric
pressure sensor, tyre pressure sensors, wheel articulation sensors,
gyroscopic sensors to detect vehicular yaw, roll and pitch angle
and rate, a vehicle speed sensor, a longitudinal acceleration
sensor, an engine torque sensor (or engine torque estimator), a
steering angle sensor, a steering wheel speed sensor, a gradient
sensor (or gradient estimator), a lateral acceleration sensor which
may be part of the stability control system (SCS), a brake pedal
position sensor, a brake pressure sensor, an accelerator pedal
position sensor, longitudinal, lateral and vertical motion sensors,
and water detection sensors forming part of a vehicle wading
assistance system (not shown). In other embodiments, only a
selection of the aforementioned sensors may be used.
[0119] The VCU 10 also receives a signal from the steering
controller 170C. The steering controller is in the form of an
electronic power assisted steering unit (ePAS unit). The steering
controller 170C provides a signal to the VCU 10 indicative of the
steering force being applied to steerable road wheels 111, 112 of
the vehicle 100. This force corresponds to that applied by a user
to the steering wheel 171 in combination with steering force
generated by the controller 170C.
[0120] The VCU 10 evaluates the various sensor inputs to determine
the probability that each of a plurality of different control modes
for the vehicle subsystems is appropriate, with each control mode
corresponding to a particular terrain type over which the vehicle
is travelling (for example, mud and ruts, sand, grass/gravel/snow).
The VCU 10 then selects which of the control modes is most
appropriate and controls various vehicle parameters
accordingly.
[0121] The nature of the terrain over which the vehicle is
travelling (as determined by reference to the selected control
mode) may also be utilised in the LSP control system 12 to
determine an appropriate increase or decrease in drive torque to be
applied to the vehicle wheels. For example, if the user selects a
target speed that is not suitable for the nature of the terrain
over which the vehicle is travelling, the system 12 is operable to
automatically adjust the vehicle speed downwards by reducing the
speed of the vehicle wheels. In some cases, for example, the user
selected speed may not be achievable or appropriate over certain
terrain types, particularly in the case of uneven or rough
surfaces. If the system 12 selects a set-speed that differs from
the user-selected set-speed (i.e. target speed), a visual
indication of the speed constraint is provided to the user via the
LSP HMI 20 to indicate that an alternative speed has been
adopted.
[0122] As described above, the LSP control system 12 is operable to
command a required amount of torque to be applied to one or more
driven wheels of the vehicle 100 in order to cause the vehicle to
travel at the user-selected set-speed. If whilst the LSP control
system 12 is active the driver depresses the accelerator pedal 161
to demand additional powertrain torque above the amount currently
demanded by the LSP control system 12, driver torque demand takes
priority and the powertrain 129 is controlled so as to meet driver
demand. In the present embodiment, if driver demand exceeds that
demanded by the LSP control system 12, the LSP control system 12
remains active, i.e. the LSP control system 12 continues to
calculate an amount of powertrain torque and brake torque that the
powertrain controller 11 and brake controller 13 should command be
applied to the driven wheels of the vehicle 100 in order to travel
at the set-speed. In this way, once a driver releases the
accelerator pedal 161, the LSP control system 12 resumes control of
vehicle speed.
[0123] It is to be understood that the LSP control system 12 may
command the required amount of torque by generating a value of a
torque parameter. The powertrain controller 11 may be configured to
develop the required amount of torque depending on the value of
this torque parameter, which may have a value that corresponds to
the required amount of torque without necessarily being equal to
the amount of required torque. Thus, for example, the LSP control
system 12 may generate a code, such as a number such as 10020,
which may correspond to a required powertrain torque of 150 Nm,
different codes being generated for different required amounts of
powertrain torque. In response to receipt of a command to generate
powertrain torque at a level of (say) 10020, the powertrain
controller 11 may therefore control the powertrain 11 to generate
150 Nm of torque. Other arrangements are also useful.
[0124] As described above, the LSP control system 12 may command
the powertrain 129 to develop a required amount of torque at a
given location, such as at an output shaft of the engine 121, at an
input shaft of the transmission 124, an output shaft of the
transmission 124, a wheel or any other suitable location. It is to
be understood that if the LSP control system 12 is arranged to
control the powertrain 129 to apply a given amount of torque at a
location other than a wheel, such as an output shaft of the engine
121, the torque delivered at a wheel may be calculated based on a
gear ratio between the engine output shaft and wheel. The control
system 12 may be operable to command the powertrain 129 to
establish a given gear ratio between a given position of the
powertrain 129 and wheel, so as to establish a desired torque at
the wheel. Thus, whilst the LSP control system 12 commands the
powertrain to generate a given amount of torque at a given position
(and may command the generation of given amounts of torque at a
plurality of locations, particularly in a powertrain 129 having a
plurality of motors such as an engine and an electric propulsion
motor), the LSP control system 12 may also be operable to ensure
that the torque delivered to a wheel is a required value by
suitable control of the gear ratio. Other arrangements are also
useful. In some embodiments, the LSP control system 12 may be
provided with data corresponding to a gear ratio between a given
position of the powertrain 129 and one or more wheels, and command
application of an amount of torque to the given position of the
powertrain 129 so as to obtain a required amount of torque at the
one or more wheels.
[0125] FIG. 7 illustrates implementation of powertrain torque
control in the vehicle 100 of FIG. 1. As can be seen from FIG. 7 an
accelerator pedal controller 161C receives an input signal from
accelerator pedal 161. The signal corresponds to pedal position and
in response to this signal the pedal controller 161C determines the
amount of torque that the powertrain 129 should be commanded to
develop. Signal pedal_tq_rq corresponding to this amount of torque
is then output to a max_pass function block 315. In some
embodiments, powertrain controller 11 may be involved in
determining the value of pedal_tq_rq in response to a value of
pedal position provided by the pedal controller 161C.
[0126] When the LSP control system 12 is active the LSP control
system 12 determines an amount of torque LSP_tq_rq that is to be
developed by the powertrain 129. The value LSP_tq_rq generated by
the LSP control system 12 is supplied to a modifier function block
320 that provides an output torque value mod_tq to max_pass
function block 315.
[0127] The max_pass function block 315 outputs to a driveability
filter 350 a signal max_out corresponding to signal LSP_tq_rq or
pedal_tq_rq in dependence on which signal has the higher value. The
signal having the higher value is output to the driveability filter
350. The driveability filter 350 is in the form of a low pass
filter and generates an output signal tq_cmd corresponding to the
actual amount of torque that is to be developed by the powertrain
129. The driveability filter is tuned to mitigate the effects of
driveline shunt so as to enhance driver enjoyment of the vehicle.
In the present embodiment, low pass filtering of powertrain torque
demand (being a value of demanded engine output shaft torque in the
present embodiment) reduces the rate of change of demanded torque
made by the driver or LSP control system thereby reducing driveline
shunt.
[0128] The driveability filter 350 provides an output tq_cmd to
powertrain controller 11 corresponding to the amount of torque to
be developed by the powertrain 129 of the vehicle 100. Driveability
filters such as that shown in FIG. 7 are well known, and may be
tuned according to the torque damping characteristics of the
vehicle powertrain 129.
[0129] The value tq_cmd output by the driveability filter 350 is
also input to the modifier function block 320. The modifier
function block 320 is shown in more detail in FIG. 9 and will be
discussed further below. In calculating the value of mod_tq, the
modifier function block 320 is configured to subtract from the
torque request value LSP_tq_rq generated by the LSP control system
12 the difference between the value of LSP_tq_rq and the currently
demanded value of powertrain torque (tq_cmd) output by the
driveability filter 350. This feature has the effect of reducing
the value of tq_cmd more rapidly. This in turn results in the
vehicle 100 slowing to the set-speed more rapidly. The modifier
function block 320 may be tuned such that the rate at which vehicle
speed slows to the set-speed corresponds more closely to that which
would be experienced if the LSP control system 12 were not active
and a user of the vehicle 100 released the accelerator pedal 161 in
order to slow the vehicle 100 to the set-speed. The amount
subtracted from the torque request value LSP_tq_rq may be be given
by the difference between the value of LSP_tq_rq and current value
of tq_cmd multiplied by a factor, for example by a factor 0.5, 2,
3, 4, 5, 10 or any other suitable value. The factor chosen may
depend on one or more characteristics of the filter 350.
[0130] It is to be understood that if the torque value applied to
the driveability filter 350 were not modified by the modifier
function block 320, the amount of time taken for vehicle speed to
fall to the target speed may be significantly longer in some
circumstances. The relatively slow response of the vehicle 100 in
reducing speed, compared with operation without the LSP control
system 12, may result in reduced driver confidence in the LSP
control system 12.
[0131] Embodiments of the present invention have the advantage
that, when the LSP control system 12 is active and a driver has
intervened to increase powertrain torque above that demanded by the
LSP control system 12 by depressing the accelerator pedal 161, the
rate at which vehicle speed slows to the target speed may be
increased following driver lift-off from the accelerator pedal 161.
The rate may be increased to correspond more closely to that which
would be experienced if the LSP control system 12 were not
functioning, and a driver were to release his or her loot from the
accelerator pedal 161 in order to slow the vehicle 100.
[0132] It is to be understood that if the vehicle 100 is travelling
at a speed of (say) 5 kph over terrain with LSP control system 12
active and in control of vehicle speed, the driver may temporarily
increase vehicle speed to (say) 15 kph whilst travelling over a
certain portion of the route. When the driver depresses the
accelerator pedal 161 to accelerate the vehicle 100, the max_pass
function block 315 allows the pedal_tq_rq signal to take priority
since it will exceed the LSP_tq_rq signal for a period of time.
During this period, the LSP control system 12 recognises that
vehicle speed has exceeded the set-speed and responds by gradually
reducing the amount of torque demanded by the system 12 in order to
slow the vehicle 100.
[0133] If the driver releases the accelerator pedal 161, the value
of pedal_tq_rq falls to a minimum torque request value. The
modifier function block 320 subtracts from the current value
LSP_tq_rq generated by the LSP control system 12 the difference
between the value of LSP_tq_rq and the currently demanded value of
powertrain torque (tq_cmd) output by the driveability filter 350,
subject to a minimum allowable value of mod_tq. The minimum
allowable value may be a negative value corresponding to powertrain
braking, typically due to engine braking and powertrain losses.
Thus the value of mod_tq may be less than the value of LSP_tq_rq,
and closer to a value corresponding to minimum powertrain torque
demand (being the value assumed by signal pedal_tq_rq in the
present embodiment). Accordingly, a rate at which the value of
tq_cmd approaches the value of LSP_tq_rq may be increased.
[0134] As noted above, the powertrain 129 may be capable of
developing (and develop in use) negative torque due at least in
part to engine over-run (compression) braking. Such braking may be
provided by the powertrain 129 due to inertia when the vehicle 100
is moving and a value of commanded torque tq_cmd is sufficiently
low.
[0135] The minimum amount of powertrain torque may correspond to a
prescribed minimum amount of torque that the powertrain can provide
under the prevailing conditions. The minimum torque may depend on a
temperature of one or more components of the powertrain such as an
engine temperature, an electric machine temperature, a gearbox
temperature and one or more other components in addition or
instead.
[0136] By way of illustration of the importance of embodiments of
the present invention, FIG. 8(a) illustrates an alternative
implementation of powertrain torque control not being an
implementation according to an embodiment of the present invention.
In the arrangement shown, the two torque demand signals LSP_tq_rq
and pedal_tq_rq described above are provided to max_pass function
block 315 in a similar manner to the arrangement of FIG. 7(a).
Signal LSP_tq_rq is generated by LSP control system 12 when the LSP
control system 12 is active, whilst signal pedal_tq_rq is generated
by accelerator pedal controller 161C in response to driver
actuation of accelerator pedal 161. The max_pass function block 315
outputs to a driveability filter 350 a signal max_out corresponding
to signal LSP_tq_rq or pedal_tq_rq in dependence on which signal
has the higher value. The signal having the higher value is output
to the driveability filter 350. As described above with respect to
FIG. 7(a), the driveability filter 350 applies a low pass filter to
the signal input thereto, generating an output signal tq_cmd1
corresponding to the actual amount of torque that is to be
developed by the powertrain 129.
[0137] FIG. 8(b) illustrates a manner in which the amount of
commanded torque tq_cmd1 varies as a function of time in one
example scenario.
[0138] At time t0, the LSP control system 12 is active and
generating a torque command signal LSP_tq_rq commanding generation
by the vehicle powertrain of an amount of torque T1. Signal
LSP_tq_rq is input to the max_pass function block 315. Also at time
t0, a driver of the vehicle has depressed accelerator pedal 161 to
demand torque T2 that is greater than T1. Consequently the
accelerator pedal controller 161C outputs to the max_pass function
block 315 signal pedal_tq_rq corresponding to a torque value T2.
The max_pass function block 315 outputs the higher of these two
values (i.e. the value of pedal_tq_rq, T2) to the driveability
filter 350.
[0139] At time t1, the driver releases the accelerator pedal 161.
The value of pedal_tq_rq therefore falls substantially to zero. The
max_pass function block 315 detects that signal LSP_tq_rq now has
the higher value, and therefore outputs signal LSP_tq_rq to the
driveability filter 350. The value of tq_cmd1 generated by the
driveability filter 250 therefore begins to fall as a function of
time, as shown in FIG. 8(b) until at time t2 the value of tq_cmd1
is substantially equal to LSP_tq_rq.
[0140] By way of comparison, the value of tq_cmd that would be
generated by driveability filter 350 in the embodiment illustrated
in FIG. 7 in substantially the same scenario is also illustrated in
FIG. 8(b). It can be seen that the value of tq_cmd falls to the
value commanded by the LSP control system 12 more rapidly when the
driver releases the accelerator pedal 161 at time t1. Where
intervention by the driver has resulted in a substantial increase
in vehicle speed, the effect of the more rapid fall in the value of
tq_cmd is that the vehicle speed reduces to the set-speed more
rapidly than it would in the arrangement of FIG. 8(a).
[0141] FIG. 9 illustrates functioning of the modifier function
block 320 of FIG. 7. As described above, signals LSP_tq_rq and
tq_cmd are input to the function block 320. The signal LSP_tq_rq is
applied to a difference function element 320a and to a summing
function element 320h. The value of tq_cmd is also input to
difference function element 320a, which outputs to a dead zone
function element 320b a value corresponding to the difference in
torque values between signals LSP_tq_rq and tq_cmd.
[0142] The dead zone function element 320b outputs a signal that is
substantially equal to the signal input thereto. However, if the
signal input thereto is within a prescribed amount of zero (whether
positive or negative), the dead zone function element 320b outputs
a signal corresponding to substantially zero torque.
[0143] The signal output by the dead zone function element 320b is
input to a minimum-pass (min-pass) function element 320c and to a
maximum-pass (max-pass) function element 320d.
[0144] The min-pass function element 320c compares the signal
received with a zero-value signal and outputs a signal
corresponding to the smaller of the two signals. Thus, if the
signal input from the dead-zone function element 320b is negative
(corresponding to a value of tq_cmd greater than LSP_tq_rq), the
min-pass function element 320c outputs this signal to a modifier
negative function element 320f.
[0145] The max-pass function element 320d compares the signal
received with a zero-value signal and outputs a signal
corresponding to the larger of the two signals. Thus, if the signal
input from the dead-zone function element is positive
(corresponding to a value of tq_cmd less than LSP_tq_rq), the
max-pass function element 320d outputs this signal to a modifier
positive function element 320f.
[0146] The modifier negative function element 320f multiplies the
signal input thereto from the min-pass function element 320c by a
prescribed factor. In the embodiment illustrated in FIG. 9 this
factor is 5 although other values are also useful. Similarly, the
modifier positive function element 320e multiplies the signal input
thereto from the min-pass function element 320d by a prescribed
factor. In the embodiment illustrated in FIG. 9 this factor is 5
although other values are also useful. The factors employed by the
modifier function elements 320e, 320f may be different in some
embodiments.
[0147] The purpose of multiplying the signals by a prescribed
factor greater than 1 is that the rate at which a speed of the
vehicle 100 approaches the target speed value may be increased.
[0148] The values output by the modifier positive function element
320e and modifier negative function element 320f are input to a
summing function element 320g which outputs a value corresponding
to the sum of the signals input thereto. The resulting value is
output to summing function element 320h. Summing function element
320h outputs a value corresponding to the sum of the signal input
from summing function element 320g and signal LSP_tq_rq.
[0149] The signal output by the summing function element 320h is in
turn input to a torque saturation function element 320l. The torque
saturation function element 320l is arranged to output a signal
corresponding to the signal input thereto but placing an upper
(positive) limit and a lower (negative) limit on the value of the
signal output thereby. For input signal values between the positive
and lower limits, the output signal value is substantially equal to
the input signal value.
[0150] The signal output by the summing function element 320h is
input to the driveability filter 350.
[0151] Embodiments of the present invention provide a control
system having speed control functionality that attempts to enhance
user enjoyment of vehicle operations. The control system allows a
user to over-ride speed control by actuating an accelerator control
to request a powertrain to develop torque exceeding the instant
value required by the speed control function to achieve or maintain
a set-speed.
[0152] If the user subsequently releases the accelerator control
without cancelling the speed control function, vehicle speed
reduces to the current speed employed by the speed control system
more quickly than might occur in systems not according to the
present invention. The system does this by reducing more rapidly
the amount of torque that the powertrain has been commanded to
develop towards a value corresponding to that required to achieve
the current set-speed.
[0153] The more rapid reduction in torque may be achieved by
reducing the value of powertrain torque input to a powertrain
torque filter (sometimes referred to as a driveability filter,
being a filter typically arranged to mitigate the effects of
driveline shunt) below the amount required by the speed control
function at a given moment in time. This causes an output of the
filter more quickly to tend towards the value of torque required by
the speed control function. Other arrangements are also useful.
[0154] It will be understood that the embodiments described above
are given by way of example only and are not intended to limit the
invention, the scope of which is defined in the appended
claims.
[0155] Embodiments of the present invention may be understood by
reference to the following numbered paragraphs:
[0156] 1. A control system for a vehicle operable to implement a
speed control function, the control system being operable to:
receive an input of a target speed at which the vehicle is intended
to travel; determine an instantaneous value of a primary target
speed torque parameter corresponding to an amount of torque that
should be developed at a given position in a powertrain in order to
control the vehicle to travel at the target speed; and filter by
means of a filter a value of a torque parameter input thereto to
generate a filtered torque parameter value, the system being
operable to command the powertrain to develop at said position an
amount of torque corresponding to the filtered torque parameter
value, wherein the system is operable to input to the filter a
secondary target speed torque parameter value determined in
dependence on the primary target speed torque parameter value and a
current value of filtered torque parameter generated by the
filter.
[0157] 2. A system according to paragraph 1 operable to determine
the value of the secondary target speed torque parameter in
dependence on a difference between the value of the primary target
speed torque parameter and the current value of the filtered torque
parameter.
[0158] 3. A system according to paragraph 1 operable wherein if the
value of the primary target speed torque parameter is less than a
current value of the filtered torque parameter, the value of the
secondary target speed torque parameter is set to a value that is
less than the primary target speed torque parameter by an amount
that is determined in dependence on the primary target speed torque
parameter value and the current value of filtered torque
parameter.
[0159] 4. A system according to paragraph 3 operable to input to
the filter a value of secondary target speed torque parameter that
is less than the primary target speed torque parameter by an amount
corresponding to the difference between the filtered torque
parameter value and the primary target speed torque parameter
value.
[0160] 5. A system according to paragraph 3 operable to input to
the filter a value of secondary target speed torque parameter that
is less than the primary target speed torque parameter value by an
amount substantially equal to the difference between the filtered
torque parameter value and the primary target speed torque
parameter value, multiplied by a factor.
[0161] 6. A system according to paragraph 1 operable such that if
the value of primary target speed torque parameter is greater than
that of the filtered torque parameter the value of secondary target
speed torque parameter input to the filter is increased to a value
above that of the primary target speed torque parameter value, the
amount of the increase being determined in dependence on the
primary target speed torque parameter value and the current value
of filtered torque parameter.
[0162] 7. A system according to paragraph 6 operable to input to
the filter a value of secondary target speed torque parameter that
is greater than the primary target speed torque parameter value by
an amount substantially equal to the difference between the
filtered torque parameter value and the primary target speed torque
parameter value.
[0163] 8. A system according to paragraph 6 operable to input to
the filter a value of secondary target speed torque parameter that
is greater than the primary target speed torque parameter value by
an amount substantially equal to the difference between the
filtered torque parameter value and the primary target speed torque
parameter value, multiplied by a factor.
[0164] 9. A system according to paragraph 1 operable to limit an
upper and lower value of secondary target speed torque parameter
input to the filter to respective upper and lower saturation
values.
[0165] 10. A system according to paragraph 1 operable to input to
the filter the higher of the secondary target speed torque
parameter value and a value of a driver demanded torque parameter
corresponding to a setting of a user-operable accelerator
control.
[0166] 11. A system according to paragraph 1 wherein the filter is
arranged to subject the value of torque parameter input thereto to
a low pass filter.
[0167] 12. A system according to paragraph 1 operable to receive a
user input of the target speed.
[0168] 13. A vehicle comprising a control system according to
paragraph 1.
[0169] 14. A method of controlling a speed of a vehicle comprising,
[0170] receiving an input of a target speed at which the vehicle is
intended to travel; determining an instantaneous value of a primary
target speed torque parameter corresponding to an amount of torque
that should be developed at a given position in a powertrain in
order to control the vehicle to travel at the target speed;
filtering by means of a filter a value of a torque parameter input
thereto to generate a filtered torque parameter value; and
commanding the powertrain to develop at said position an amount of
torque corresponding to the filtered torque parameter value,
wherein filtering by the filter the value of torque parameter input
thereto comprises filtering a secondary target speed torque
parameter value determined in dependence on the primary target
speed torque parameter value and a current value of filtered torque
parameter generated by the filter.
[0171] Throughout the description and claims of this specification,
the words "comprise" and "contain" and variations of the words, for
example "comprising" and "comprises", means "including but not
limited to", and is not intended to (and does not) exclude other
moieties, additives, components, integers or steps.
[0172] Throughout the description and claims of this specification,
the singular encompasses the plural unless the context otherwise
requires. In particular, where the indefinite article is used, the
specification is to be understood as contemplating plurality as
well as singularity, unless the context requires otherwise.
[0173] Features, integers, characteristics, compounds, chemical
moieties or groups described in conjunction with a particular
aspect, embodiment or example of the invention are to be understood
to be applicable to any other aspect, embodiment or example
described herein unless incompatible therewith.
* * * * *